With respect to techniques for production of hydrogen, there are by-product hydrogen from other industrial processes, e.g., from processes manufacturing iron and steel, hydrogen produced by reforming coal and petroleum, etc. Hydrogen produced by such processes is strongly equipment-dependent and lack of convenience in the aspect of simple utilization thereof at proper timing.
On the other hand, as a means for easily obtaining hydrogen, there is a method of utilizing a decomposition reaction of ammonia. The reaction formula is as follows: NH3→0.5N2+1.5H2. Since this reaction is an endothermic reaction with a large amount of 10.9 kcal/mol, it is required to supply the reaction heat from the outside of the reaction system. As a method for supplying the reaction heat, there is an autothermal reformer (ATR) involving combusting raw material ammonia or a portion of hydrogen produced by the decomposition reaction of ammonia and using the combustion heat as the reaction heat for ammonia decomposition (Patent Document 1, Non-Patent Document 1). The combustion reaction is as follows: NH3+0.75O2→0.5N2+1.5H2O and H2+0.5O2→H2O. As a catalyst used for ATR, there are a catalyst obtained by supporting Ru on alumina (Patent Document 1) and a catalyst obtained by supporting Pt and Rh on alumina (Non-Patent Document 1).
However, in the case of using these catalysts, it is difficult to control the reaction in accordance with the catalyst composition and it is not easy sometimes to steadily obtain hydrogen in a constant concentration. Further, due to alteration of catalyst layer temperature, an ammonia reformer may possibly be damaged or the catalysts may possibly be deteriorated.
Due to these factors, the ammonia decomposition reaction becomes unstable. If the decomposition ratio is insufficient, a large quantity of ammonia remains in the gas after the reaction and it results in provision of a fuel with an inferior quality as a hydrogen fuel.